I am having a similar problem. High oil consumption, but no smoke. I check at start up, I watch at idle and I have even had the wife drive up and down the road and I have seen no smoke. There is not a drop on the garage floor.
Jim Anderson mentioned the crank vent. Can you elaborate on this. In the winter I sometimes get a sludge build up, which I understand is moisture not burned off, and primarily caused by improper crankcase ventilation. I really have no understanding on this subject. Can this cause high oil consumption too? Car is '86 420SEL
1995 E420 - retired
1986 420SEL - retired